The present invention pertains generally to multistage pumps and more particularly to the case construction of multi-stage, volute-type centrifugal pumps.
It has been the practice in the art to provide an inner pump-case construction that is axially split at all pump stages, which consist of a first stage and one or more booster stages. It is known to employ the relatively high pressure in a discharge chamber formed within an outer case and surrounding the booster stages as a means for forcing the axially split booster-stage case sections together to form a fluid-tight joint between case sections. However, since the first-stage case section is provided within a chamber in fluid communication with a relatively low pressure inlet, it is not possible to form a fluid-tight joint between the axially split inner case sections employed at the first stage in prior art pumps. Rather, it has been the practice to employ bolts or other fastening means to secure such first-stage inner case sections together in a fluid-tight manner.
The seal formed by such bolting arrangements is subject to deterioration capable of affecting the performance of the pump and can eventually render the pump inoperable. Those skilled in the art will appreciate that there are additional problems with such bolting arrangements, especially for pumps that develop very high energy per stage. For example, there are practical limitations on the number and size of bolts that can be used to seal the joint between the axially split inner case sections of the first stage due to, among other things, design considerations in minimizing hydraulic flow interference between the outer-case inlet and the first stage.
It would be desirable, therefore, to provide a case construction for a double-case, multi-stage pump which would overcome the aforementioned problems encountered in the prior art and thereby eliminate the eventuality of pump failure due to leakage at the joint between the first-stage sections of the inner case assembly.